The present invention relates to an optical disc apparatus.
In recent years, an optical disc apparatus was put into practical use, which can record/reproduce information onto/from an optical disc apparatus. In such optical disc apparatus, there is a problem of tracking out, i.e., an optical beam cannot follow or track the information track. And, within the optical disc apparatus is already known a tracking out detection function, i.e., for detecting that the optical beam cannot follow the information track.
In the following Patent Document 1 is described, in the column 0002 thereof, “Within the conventional optical disc apparatus for exclusive use of readout, the tracking out is detected through observing continuity of the address information, which is read out from the disc. However, when applying this method therein, the recording-type optical disc apparatus takes time from ten and several milliseconds to several tens milliseconds until when it detects that, if the tracking out is generated during the recording operation; i.e., there is a problem of taking a relatively long time, and therefore double-writing is done on the neighboring track.”
In the following Patent Document 2 is described, in the column 0018 thereof, “The tracking out detector means has a comparator means for comparing an input signal with a positive threshold value and a negative threshold value to a signal having a predetermined level, when the input signal is larger than the positive threshold value and when it is smaller than the negative threshold value, and a counter for measuring a period, during when the signal having the predetermined level is outputted from the comparator means, for each predetermined time-period, being characterized in that determination is made that the optical beam is in the condition of not following the information track, when the counted value comes up to be larger than a predetermined threshold value, and thereby outputting a tracking out signal.”
Also, in the following Patent Document 3 is described, in the column 0022 thereof, “For example, in case where the amplitude of a tracking error signal comes to be narrower than the width between the positive and negative comparison values, as is shown in FIG. 9(A), due to any reason, it is impossible to detect the tracking out at all.” Also, in the column 0025 is described, “In this manner, according to the fourth embodiment, it is possible to bring the tracking error signal and the positive and negative comparison values into correct relationships, by creating the tracking out condition through conducting a track jump, and changing the amplitude of the tracking error signal while monitoring the tracing error signal, and therefore it is possible to detect the tracking out, with high accuracy.”
In the following Patent Document 4 is described, in the column 0016 thereof, “When the lens shift amount of the objective lens 4a come to be large during the tracking control, as is shown in FIG. 20, an amount of the amplitude of the tracking signal, which can be obtained, comes down to be small.”
Further, in the following Patent Document 5 is described, in the column 0034 thereof, “In FIG. 10 are shown estimations of de-track amounts, which are generated in the first and second embodiments, with respect to shift of the objective lens, during when executing the tracking control in accordance with the DPP method. In the first embodiment, there is generated a large de-track accompanying with the shift of the objective lens.”
Also, in the columns 0028 and 0029 of the following Patent Document 6 is described, “Also, tracking/offset fluctuates due to the shift of the objective lens 15. This also has characteristics of changing depending on a direction θ of astigmatism. Also, if the optical system in the optical pickup 10 has the astigmatism, there is a tracking/offset changing in relation to the magnitude of this astigmatism and also the magnitude of the lens shifting of the objective lens 15.”
In the column 0005 of the following Patent Document 7 is described “(4) comprising an observer circuit, having an actuator for driving the objective lens, which is mounted on the carriage, a lens shift detector means for detecting an amount of shifting of the objective lens as a lens shift signal, a magnetic recording head connected with the carriage, so as to face the objective lens putting the recording medium therebetween, and a window comparator for observing the lens shift signal and detecting the fact that the objective lens exceeds a predetermined shift amount, and (5) being constructed in such a manner that upon the level of the lens shift signal when the objective lens reaches to about 0.3 mm, in relation to (4) mentioned above.”